The present invention concerns a transmission unit, in particular for motor vehicles, with a housing, with an input drive shaft, with an output shaft and with a arrangement for changing the gear ratio between said two shafts, which arrangement exhibits a continuously variable, gear drive.
Continuously variable gear drives (hereinafter xe2x80x9cCVTxe2x80x9d) in the form of stepless transmissions or friction clutch drives are known in a multiplicity of variations. For instance, DE 198 44 374.9 of the Applicant describes a CVT drive which possesses a first V-pulley pair on an input drive shaft and a second V-pulley pair on an output drive shaft, whereby each V-pulley pair comprises a first pulley fixed in the axial direction and a second V-pulley which is slidable in an axial direction, otherwise designated respectively as a primary pulley and as a secondary pulley. Between the V-pulley pairs runs a stepless organ, namely a steel thrust belt. The displacement of the primary pulley or the secondary pulley is done by means of a pressure medium with an aid of an electronic control apparatus which, through electromagnetic positioning elements and hydraulic valves regulates the range of pressure of the positioning space of the primary pulley and the secondary pulley.
A friction disk transmission is, in an exemplary way, described in the WO 99/05433. This transmission possesses input and output disks, which are assembled pairwise to one another and the mutually facing, inner surface of each of these disks is toroidal in shape. The transmission has likewise, friction disks installed between the pairs of input disks and output disks. These friction disks stand in friction contact with the inner surfaces of both the input disks and similarly with the output disks and transfer the torque delivered to them from the input disks over to the output disk by friction-based contact. When this is done, the rotational speed of the friction disks lies just so much higher, the greater the separating distance is between their touching zones with the input disk and the axis of rotation. The rotational speed of the output disk, on the other hand, is just so much greater, the closer the touching zone between the friction disk and the output disk on the axis of rotation is, by means of pivoting the friction disks on this account, the speed of rotation of the output disk can be adjusted in a stepless manner as desired. For this purpose, the friction disks are mounted on a carrier which is controllable by means of a pivoting apparatus. The two input disks of the two transmission units are, in this case, so affixed as to turn with a torque shaft, while the two output disks of the two transmission units, which are in mirror image of one another and placed beside one another in the transmission, are placed on a common bushing, which is set to rotate on the torque shaft. The torque shaft is crossed by an input shaft, which is connected with a starting element of the motor vehicle, for instance, a torque converter or a wet starting clutch of the driving machine of the motor vehicle.
The U.S. Pat. No. 5,888,161 describes an automatic transmission for a motor vehicle, which exhibits a CVT transmission, the input shaft of which is connected with a starting element in the form of a hydrodynamic converter, and the output shaft of which is connected to an intermediate shaft. Between the hydrodynamic converter and the CVT-transmission, a planetary gear set is provided which, first, is connected to the input shaft and, second, connected to a countershaft. The countershaft runs on to a gear-pair, which is subordinate to the CVT and which holds to a constant transmission ratio. The gear-pair possesses a first output shaft for the rear axle drive as well as a second output drive shaft which the CVT transmission converts for the front axle drive.
In this way, a 4-wheel-drive is created by the usage of a CVT-transmission, in the case of which, the starting of the motor vehicle is carried out by a by-pass to a gear reduction package which is placed in the CVT transmission. In this way, upon starting, the necessary large starting torque is transmitted exclusively through a gear tooth connection to the axles and not through the CVT transmission. Further a gear up-shifts are likewise shifted at a fixed gear ratio, however, with the intervention of the CVT. The apportionment of the torque between the front axle and the rear axle remains in this arrangement in a fixed ratio to one another for all gear shift positions.
The EP-A-743 218 discloses a four-wheel drive for a motor vehicle with the use of a friction disk transmission. A planetary gear set, or a differential is coupled thereto, which allows an output shaft for the rear axle and an output shaft for the front axle of the motor vehicle. Along with this, in a controllable manner, a division of the torque between the rear axle and the front axle of the motor vehicle is made possible, whereby, the friction disk transmission possesses two transmission units, the torques of which, are transferred, respectively, by an corresponding output shaft. The resulting two shafts are independent of one another and stand in connection with one another only through the differential. The torque evolved by the first transmission unit is, in part, conducted through the differential of the forward axle and, in part, to the rear axle of the motor vehicle. The torque yielded by the second transmission unit is completely and without any intermediate shifting of the differential, conducted to the rear axle. In this way, a torque apportioning of about 25% is transmitted to the front axle and 75% to the rear axle, as is, in particular, of advantage for heavy trucks.
The friction disk transmission employed here requires, first, an increased expenditure for construction, since in this case two compressor apparatuses and two output torque devices are required for the friction disk transmission. Second, two bearings and an apparatus in order to adjust the gear ratio for the rear wheel axle to be in accord with the motor are necessary.
The purpose of the present invention is to create a transmission unit especially for a motor vehicle which, besides the stepless transmission, possesses a multiplicity of necessary components required in addition for the drive of a vehicle and which can be installed both as a transmission unit for the drive of an axle as well as a transmission unit for the drive of two axles, that is, a forward axle and a rear axle of a motor vehicle.
The transmission unit in accord with the invention possesses a housing, with one input drive shaft and with at least one output shaft, whereby, in the housing the following components are to be found:
a starting element connected to the input shaft,
a stepless transmission connected to the starting element,
a transfer gear set connected to the stepless transmission, which possesses
a first output drive shaft, which is connected to the rear axle, and
a second output drive shaft which is connected to the front axle through a
differential for front axle drive, whereby, at least one of the half-axles, between the differential and the forward axle drive and its corresponding front wheel, penetrates the housing between the starting element and the stepless transmission.
The stepless transmission can, in this matter, be a CVT or a friction disk transmission, whereby the latter has a type of construction, as has been described in the previously mentioned WO 99/05433, wherein the two transmission units are connected by means of a common output with the transfer drive, so that the construction expense and complexity for the friction disk transmission is made less than in the case of the friction disk transmission described in EP 0 743 218 which was also mentioned in the introduction.
The transfer gear set, according to the invention, is integrated into the housing and advantageously possesses a mid-differential for the splitting of the torque to the rear axle and to the front axle for the motor vehicles provided with this transmission unit, in so far as the transmission unit is to assure a 4-wheel drive of the vehicle. Just as well, it is also possible to so design the transfer gear set that the entire torque delivered from the stepless transmission to the transfer gear set is exclusively transferred to the rear axle of the vehicle by means of bypassing the connection between the transfer gear set and the front axle differential, so that the invented transmission unit is usable for the drive of the rear axle.
By the invented integration of a multiplicity of components in one single housing, not only is the need for installation space substantially reduced, but also, as has been mentioned before, the advantage is gained that the transmission unit can be employed as a standard transmission unit or a 4-wheel drive unit, whereby the manufacturing costs and the upkeep of the bearings are substantially reduced. The adjustment of the axle gear ratio is done between the transfer gear set and the stepless transmission. The design of the distribution of the torque permits adjustment for the torque respectively in the transfer gear set in accordance with the demands in the case of a 4-wheel drive.